This invention relates to magnetic imaging and more particularly to the creation of improved latent magnetic images on magnetic substrates.
There has recently been discovered a magnetic imaging system which employs a latent magnetic image on a magnetizable substrate which can then be utilized for purposes such as electronic transmission or in a duplicating process by repetitive toning and transfer of the developed image. Such latent magnetic image is provided by any suitable magnetization procedure whereby a magnetized layer of marking material is magnetized and such magnetism transferred imagewise to the magnetic substrate. Such a process is more fully described in U.S. Pat. No. 3,804,511 to Rait et al., which patent is hereby incorporated by reference.
As is disclosed in said patent, an optical image can be reproduced by first reducing it to a graphical image but employing a magnetizable marking material. Such magnetizable material is typically electroscopic toner comprising a ferromagnetic material which, after image formation is susceptible to magnetization. There is thus formed an imagewise pattern of magnetization which pattern is then transferred to a magnetic substrate by any one of several methods as disclosed in said patent. Preferably, the magnetization in imagewise pattern is produced in a magnetic substrate by the anhysteretic method whereby the magnetized graphic image is brought into intimate contact with a magnetic substrate and while in contact is subjected to an A.C. signal. The magnetic substrate is thereby magnetized in image configuration in accordance with the graphic image. Other methods of utilizing the magnetized graphic image for producing a latent magnetic image are also disclosed such as by providing intimate contact between the graphic magnetic image and a previously uniformly magnetized substrate and applying an erase signal through the graphic image support thereby applying the magnetic image as a shunt for the erase signal. There is thus produced by selective erasure in background areas a latent magnetic image in those areas shunted by the magnetic graphic image. Various other methods of providing such latent image utilizing a previously formed magnetizable graphic image are disclosed in the patent referred to above.
One desires to form a latent magnetic image having the highest possible degree of magnetization such that its detection by any of the several methods is facilitated. The process variations inevitable in prior art imaging systems whereby the magnetizable graphic image is produced causes variations in toner depth, unevenness of the surface of the image and background problems. Such variations make difficult the creation of high quality latent magnetic images by the method referred to above.